Concanavalin A binding of soluble neutral maltase-glucoamylase in suckling rat intestine

Molecular nature of three liver alkaline phosphatases detected by drug administration in vivo: differences between soluble and membranous enzymes

1. Activities of alkaline phosphatase, liver-membranous, liver-soluble and serum-soluble, were dramatically induced in dogs by treatment with both phenobarbital and brovanexine. The treatment induced a 17-fold increase in membranous, a 155-fold increase in soluble, and a 105-fold increase in serum alkaline phosphatases. 2. There was no difference in the enzymatic behavior of the three forms of alkaline phosphatase, on heat stability, amino acid inhibition and optimum pH. 3. When the three alkaline phosphatases were treated initially with n-butanol, their apparent molecular size was identical. After treatment with phosphatidylinositol-specific phospholipase C, the liver-soluble and serum-soluble alkaline phosphatase were of the same molecular size. Liver-membranous alkaline phosphatase, however, was larger in molecular size than the other two forms, suggesting a difference between soluble and membranous alkaline phosphatase forms. 4. In terms of the sugar moiety of the three alkaline phosphatase forms, the membranous enzyme showed more of the higher affinity fraction and less of the lower affinity fraction of concanavalin A, compared with the soluble enzymes. 5. Consequently, it is possible that the membranous enzyme may be solubilized by an enzyme such as phosphatidylinositol-specific phospholipase C and modify further the sugar moiety of alkaline phosphatase molecules, resulting in serum alkaline phosphatase transfer from the soluble enzyme in liver.

Biosynthesis and transport of glycoproteins in the small intestinal epithelium of rats. I. Developmental change and effect of hypophysectomy

The biosynthesis and intracellular transport of glycoproteins in duodenal absorptive cells of intact rats at 6 and 24 days and hypophysectomized rats at 24 days of age were studied after 20 min intralumenal pulse-labeling of D-[3H]galactose, L-[3H]fucose, or D-[3H]mannose. Autoradiographic studies showed that the incorporation of sugars increased significantly in intact rats between 6 and 24 days. When rats were hypophysectomized at 6 days of age, the intestinal epithelium at 24 days incorporated D-[3H]galactose at a level significantly lower than that of intact rats at 24 days. Hypophysectomy also interfered with the developmental increase in D-[3H]mannose, but not in L-[3H]fucose, incorporation. Biochemical study indicated that the radioactivity in the lipid-free acid-precipitable glycoproteins in the intestine of 24-day-old intact rats at 20 min after D-[3H]galactose injection was 129% and 97% higher than that in 6-day-old rats and in 24-day-old hypophysectomized rats, respectively. The patterns of intracellular transport of newly synthesized galactosylated or fucosylated glycoproteins in all animal groups were similar; the labeled glycoproteins were initially present in the Golgi and were transported through the smooth endoplasmic reticulum to either the lateral membrane or the brush-border membrane within 60 min after the injection of labeled sugars. The proportion of labeled glycoproteins that migrated to the brush-border membrane, however, increased about twofold in the intact rats between 6 and 24 days of age at 60-240 min after D-[3H]galactose injection. Hypophysectomy interfered with developmental increase in the transport of glycoproteins from the apical cytoplasm to the brush-border membrane. It was concluded that the incorporation of monosaccharide precursors into glycoproteins and the proportion of newly synthesized galactosylated or fucosylated glycoproteins transported to the brush-border membrane increase during postnatal development. The developmental changes are regulated, at least partially, by the pituitary gland.